Tecnico

Chemical Engineering Science 60 (2005) 6815 – 6823
www.elsevier.com/locate/ces

Experimental simulation of distillation concentration profiles using batch
apparatus: Column stripping section
Jean Lubilanji Mulopo, Diane Hildebrandt, David Glasser∗ , Brendon Hausberger,
Shezaad Kauchali
Centre of Materials and Process Synthesis, School of Process and Materials Engineering, University of theWitwatersrand, Private Bag 3,
Wits, 2050, Johannesburg, South Africa
Received 30 June 2004; received in revised form 11 May 2005; accepted 11 May 2005
Available online 25 July 2005

Abstract
It has been shown that distillation column rectifying profiles can be measured experimentally in a batch boiling apparatus using a
combination of equilibrium boiling, vapour removal and the addition ofmaterial of the distillate composition (Chemical Engineering
Science, 2003, 58, 479). The problem of using this concept for stripping profiles is that in order to follow the concentration profiles one
needs to remove material of the bottom composition while retaining equilibrium boiling conditions. This cannot be effectively implemented
as the bottoms composition is not produced in the apparatusand that the removal of this material would not be possible under equilibrium
conditions.
In this paper, we re-examine the differential description of the distillation stripping section and using vector concepts show that the
removal of material of the bottoms compositions is equivalent to the addition of material of a composition that varies in a mathematically
predictable manner with time.This feed policy has been implemented experimentally and it is shown that stripping section profiles can be measured with reasonable
accuracy in a batch still. This work verifies and validates experimentally the concept that separation and mixing are opposite vectors
phenomena (On the behaviour of reactive distillation systems. Ph.D. Thesis Norwegian University of Science and Technology,Trondheim.)
and also offers an opportunity to combine computer software and experimental simulation to simplify troublesome calculations and help
reduce computational time.
2005 Elsevier Ltd. All rights reserved.
Keywords: Distillation concentration profiles; Column rectifying section; Column stripping section

1. Introduction
Distillation column concentration profiles can be used to
assist the designengineer in designing complex distillation
columns (Doherty and Malone, 2001). However, to be able
to determine the feasibility of a required separation in a distillation column, one need to determine the column profiles
for both the rectifying and stripping sections. In traditional
distillation design the general short-cut technique has been

∗ Corresponding author.

E-mail address:dihil@comps.wits.ac.za (D. Glasser).
0009-2509/$ - see front matter
doi:10.1016/j.ces.2005.05.061

2005 Elsevier Ltd. All rights reserved.

to determine the liquid composition profiles from the rectifying section calculated from the distillate down the length
of the column and the liquid composition profiles for the
stripping section calculated from the bottoms up the column. A separation isconsidered to be feasible if these liquid profiles intersect. Current techniques to determine these
profiles use simulator packages or require laboratory-scale
plot plants. These two methods raise major concerns among
the engineers.
The time consumed and the lack of insights into solutions
do not always allow the designer to rely completely on
computing methods. A combination of computer packagesand simple experimental techniques can be a simplification.
On the other hand, the costs associated with pilot plants

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J. Lubilanji Mulopo et al. / Chemical Engineering Science 60 (2005) 6815 – 6823

and the poor extrapolation to full scale has led designers not
to consider this alternative (Tapp et al., 2003).
The simulation of these profiles can be substantially
simplified...